It is known that condition changes and diseases in the living body appear in variations of body fluid, for example, blood, urine, saliva and the like as biological reactions. Then, a change in physical condition is monitored and diseases are detected, by measuring and analyzing components contained in body fluid.
Particularly, blood tests measuring blood components are widely conducted as an effective means for investigating diseases and as a means for health management.
In measuring a component in body fluid, it is required to reliably collect a necessary amount of body fluid. For example, in a collection instrument having a body fluid collecting part, a developing part thereof and a determining part thereof disposed so as to connect sequentially on a plate-like base, body fluid collected by the collecting part is introduced to the determining part through the developing part. Further, a collection instrument in which an absorbing part, a liquid retaining part, and in some cases, further a recovering part are disposed sequentially on a hydrophilic absorbent is also suggested. In these body fluid collection instruments, body fluid is collected by allowing an absorbent composed of fiber to absorb body fluid. In these collection instruments, blood absorbed by the absorbent is not separated and specific components are analyzed and determined at the determining part, alternatively, the absorbent having absorbed blood is immersed in separating liquid, then, plasma is separated from the absorbent and specific components are analyzed. The former means is not suitable for analysis of arbitrary components in serum or plasma. In the latter means, an operation for obtaining plasma components is complicated. In addition, the amount of a specific component in blood cannot be measured correctly in either method.
In addition, there is a suggestion on a micro blood sampling tool using a disposable pipette in which a dropper tube and a flexible cap communicate (Patent document 1). In this blood sampling tool, liquid is temporarily sucked, then, the sucked liquid can be released, but the collected blood cannot be kept under the same state, thus, the liquid cannot be preserved and separated.
Further, a blood collection kit comprises a blood collecting tool and a blood collecting bottle is suggested (Patent document 2). This blood collecting tool is composed of a cylindrical liquid absorbing unit for performing temporal liquid absorption disposed at the end and containing blood coagulation preventing liquid and a pushing unit which pushes the rear surface of the liquid absorbing unit to separate the liquid absorbing unit, while, a chemical solution is contained in the blood collecting bottle. When the pushing unit of the blood collecting tool is pushed and the blood collecting tool is pushed into the blood collecting bottle, blood is eluted from the end of the blood collecting tool into the chemical solution. Since the collected blood is mixed in the chemical solution, however, plasma of the collected blood cannot be separated, and additionally, the amount of a specific component in the blood cannot be measured correctly.
The blood test using serum derived from collected blood includes conventionally operations such as blood collection using a syringe with needle and a blood collecting tube, and according to circumstances, transfer to a centrifugal separation vessel, centrifugation, serum suction, and application of the sucked serum to an automated analyzer.
However, blood collection by a syringe needle places a heavy burden such as strong pain and the like on a person to be blood-collected. Particularly in infants and elderly people, and not healthy people, blood collection is difficult in some cases, since blood vessel is narrow, and correct tapping of a syringe needle into blood vessel from the outside is difficult, and the like.
Since blood test with a very small amount of blood has become possible recently, conventional blood collecting methods using a syringe with needle and a blood collecting tube have a problem that unnecessarily large amount of blood is collected to force a person to be blood-collected an excessive burden and most of the collected blood is not necessary for the examination.
In contrast, a currently suggested blood collection instrument for collecting a very small amount of blood has a problem that preparation of serum or plasma suitable for use in the later blood test like in the conventional blood collecting method using a syringe with needle and a blood collecting tube is impossible.
As an instrument for collecting a very small amount of peripheral blood, a blood collecting tube composed of a capillary tube is conventionally known. Further, a tube having a cylinder-like structure having a nozzle portion in the form of a capillary tube is suggested, in which blood held in a capillary tube is easily taken out without transferring blood collected in a capillary tube to a reservoir (Patent document 3). In this technology, a cap for plugging the nozzle portion in the form of a capillary tube is prepared, the nozzle of a capillary tube is plugged using the cap after collecting blood, and it is placed in an outer vessel in the form of a cylinder. Alternatively, a cap structure for the nozzle is prepared in the outer vessel, and when the capillary tube is inserted into the outer vessel, the nozzle is plugged. Under this state, centrifugation and transfer are possible.
An instrument using a capillary tube is suggested as a blood collection instrument causing a small amount of blood collection, however, the collected blood is subjected to a centrifugal treatment thereafter.
In the blood collection instrument as suggested in Patent document 3, when centrifugation is conducted, respective fractions of blood cells and serum are constantly in contact at the liquid level, and for example, glucose contained in serum is consumed as a nutrient material of red blood cells, thus, if transportation takes a long period of time, correct quantification becomes difficult. That is, measurement should be carried out immediately after blood collection, thus, this instrument is not suitable for storage and preservation.
Furthermore, though blood test with a very small amount of blood has become possible as described above, the amount of a sample required should vary depending on conditions such as target test items, apparatus and reagents to be used, thus, collecting amount should be changed depending on conditions, for conducting blood collection of an optimum amount while avoiding blood collection of unnecessarily large amount.